It is well known in the gas turbine engine art to utilize a centrifugal fuel pump for normal operation and a separate (e.g., positive displacement) pump to supply enough fuel to start the engine. The positive displacement pump is used during startups since a properly sized centrifugal pump normally cannot supply sufficient fuel pressure while the engine is rotating at starting speeds. The separate pump is switched out after the engine reaches operating speed.
Typical prior actuation systems use a separate high pressure pump which uses oil, either the engine lubricating oil or a hydraulic fluid to control the actuators which control the configuration of the exhaust nozzle. The use of a separate fluid to control the nozzle actuators results in the necessity of including an additional, dedicated actuation pump. It would, therefore, be advantageous to provide a fuel system including both a centrifugal main pump and a separate positive displacement actuation pump, wherein, the actuation pump is a backup for the centrifugal engine fuel pump, and the centrifugal engine fuel pump is a backup for the actuation pump.